Consequently, these compositions may be in the form of and may act as food supplements, dietetic bases or medicinal preparations proper, according to whether they are intended to act as bases or prophylactic treatments or as therapeutic preparations proper, depending on the particular individuals for whom the composition is intended.
Three different types of sphingomyelinase (SMase) have so far been identified.
There is an acidic sphingomyelinase, which is a lysosomal enzyme (with an optimum pH of 4.5-5), deficiency of which causes Niemann-Pick disease, and there is a neutral sphingomyelinase, with an optimum pH of 7.5, for which two iso-forms have been described. One of these iso-forms is located in the cytoplasmic membrane and depends on magnesium, while the other is contained in the cytosol and is independent of cations. Both the acidic and the neutral sphingomyelinase are found in many tissues and cells and are ubiquitous enzymes, regulating numerous cell functions.
The third type is called alkaline sphingomyelinase, because it is mainly active at pH 9. It is independent of magnesium and has been found both in intestinal brush borders and in the bile. Alkaline sphingomyelinase does not occur in the stomach, duodenum or pancreas but it is found in the intestine, especially in the distal part of the jejunum. A marked alkaline sphingomyelinase activity has also been observed in the colon and the rectum. High levels of alkaline sphingomyelinase are also found in the bile, but this seems to be peculiar to human beings. This twofold source of sphingomyelinase makes human beings very efficient in comparison with other creatures as regards the hydrolysis of sphingomyelin (SM) introduced via the diet. It has hitherto been thought that alkaline sphingomyelinase cannot be produced by intestinal bacteria, because no differences have been found between conventional and germ-free animals (see R. D. Duan, Scand. J. Gastroenterology, 33 (1998) pp. 673-683).
Apart from the alkaline sphingomyelinase that is present in the intestine and that present in the bile, no other alkaline sphingomyelinases are known that could be used to produce compositions intended for nutritional, dietetic or strictly therapeutic use. Moreover, acidic and neutral sphingomyelinase cannot be employed owing to their differing characteristics (see the following table).
TABLENeutral SMaseAlkaline SMaseAcidic SMasecytoplasmichuman intestineLocationlysosomesmembraneand bileOptimum pH5.57.49Mg++-dependenceNoYesNoTrypsinNoNoYesresistanceThermal<40° C.—<50-60° C.stabilitySubstrateendocytic SMmembrane SMSM in food
The use of sphingomyelinase for cosmetic and dermatological purposes is already known.
Japanese Patent No. 63 216,813 describes cosmetic compositions that contain sphingomyelinase and are intended for counteracting the physiological decrease of this enzyme that occurs in the skin on ageing, and for promoting its transformation into ceramide which, in turn, has a beneficial moisturizing effect on the epidermis.
International Patent Application PCT WO 98/22,082 describes the use of sphingomyelinase for the preparation of dermatological compositions suitable for treating skin disorders such as dermatitis, psoriasis, ichthyosis and similar conditions. Furthermore, this PCT application describes the preparation of sphingomyelinase from strains of Gram-negative bacteria, Gram-positive bacteria and lactic acid bacteria, with clear advantages over the previously known processes, which use the organs of higher animals, such as the brain and liver, as starting materials.